Abstract of research plan. We will study the angiotensin I converting enzyme or kininase II purified from human lung. We will improve and simplify the currently employed purification procedures, elicit antibodies to the human enzyme and employ the antibody in radioimmunoassay. The activity of the enzyme will be studied in purified soluble form as well as in membrane-bound form. The hydrolysis of a variety of peptide substrates by the insoluble enzyme, will be established. Natural occurring inhibitors of the enzyme will be characterized.